Transmix is created when products of different specifications are shipped sequentially on a pipeline. The pipeline operator might ship a volume of distillate (aviation turbine fuel or Ultra Low Sulfur Diesel, etc.) followed by a volume of gasoline intended for automobiles. When these two products meet in the pipeline at an interface, a quantity of off-specification product referred to as “transmix” is created. There is no mechanical buffer used to keep the two products from mixing and becoming contaminated at this interface. The transmix does not meet approved specifications for most fuel products and cannot be used in commerce.
In the United States, pipelines ship motor gasoline, diesel fuel, jet fuel, naphtha's, LPG, diluent, butane, propane, pentane, and other hydrocarbon products on the same clean pipeline. Both refineries and petroleum terminals ship on these common carrier pipelines, in varying sizes or batches. A batch is the volume of a product shipped on the pipeline meeting a pre-defined set of product specifications. The pipeline companies and various regulatory authorities publish product specifications that shippers on the pipeline are required to meet before introducing their products into the pipeline. The pipeline company must ensure that the products it eventually releases into commerce meet these specifications. The shippers provide a certified analysis of the products to the pipeline company to verify the products meet the minimum or maximum specifications published by the pipeline company.
All multi-product pipelines create a volume of transmix that is not marketable for use in commerce. This transmix may be composed, for example, of previously certified gasoline (including previously certified gasoline blend-stocks that become gasoline solely upon the addition of an oxygenate), distillate fuel (such as diesel, aviation fuel, kerosene and heating oils), and other certified product types. The problem is particularly acute when diluents, ultra-low sulfur diesel, aviation turbine fuel, and gasoline are shipped next to each other.
The United States Environmental Protection Agency (“EPA”) defines interface and transmix in regulations at 40 C.F.R. 80.84, and prescribes processes that pipeline operators must follow to dispose of transmix. This transmix must typically be re-processed before it can once again be marketed in commerce. The value of transmix is thus lower than the hydrocarbon products from which the transmix derives, and it is in the commercial interest of pipelines and pipeline shippers to minimize this transmix.
Presently, pipeline operators monitor the specific gravity, flash point, haze and color of batched products to determine when transmix is present and when on-specification products are in the pipeline. Based on their standard operating procedures, the pipeline operator will direct the transmix to a transmix storage tank when it reaches a particular juncture on the pipeline, where it can be stored for eventual shipment to a transmix processing plant. Once the transmix has been completely diverted from the pipeline, and on-specification products are once again flowing past this juncture, the operator will resume the product flow through the pipeline and direct the on-specification product to other tanks in the tank farm for eventual distribution to customers and in commerce. The more time it takes for the pipeline to make the interface cut, the more transmix that is created. Again, it is in the best interest of the pipeline company to create the smallest amount of transmix as possible.
Accordingly, it is an object of the present invention to reduce the volume of transmix created on petroleum pipelines, and to maximize the retention of on-specification products for commercial distribution.
It is another object to provide methods of managing transmix that minimize the volume of transmix production during pipeline transportation while ensuring that on-specification products remain within their prescribed specifications.
A still further object is to automate the process of transmix diversion, so that transmix is diverted from the pipeline using consistent numeric criteria, and reducing the need for guesswork and significant human intervention.